doc: getting_started: Remove Linux distro versions
doc: getting_started: Remove Linux distro versions

Remove the version numbers from the distribution listings, since those
get outdated quickly and on top of that they are causing confusion due
to those being now too old to contain recent versions of CMake and DTC.

Signed-off-by: Carles Cufi <853081dc8dca4fe6a7e3c984752718b5db36e060@nordicsemi.no>

nashif/zephyr,Vudentz/zephyr,galak/zephyr,galak/zephyr,galak/zephyr,finikorg/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,galak/zephyr,nashif/zephyr,finikorg/zephyr,finikorg/zephyr,nashif/zephyr,finikorg/zephyr,nashif/zephyr,Vudentz/zephyr,nashif/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr